Solid state fabrication of hard, high melting point, heat resistant materials



United States Patent 3,000,734 SOLID STATE FABRICATION 0F HARD, HIGH MELTING POINT, HEAT RESISTANT MA- TERIALS Nicholas J. Grant, Winchester, Mass., and Claus G. Goetzel, Hastings on Hudson, and Eugene J. Kalil, New York, N. assiguors to 134 Woodworth Corporation, a corporation of New York No Drawing. Filed Oct. 11, 1956, Ser. No. 615,224 6 Claims. (Cl. 75-201) The present invention relates to heat resistant metal products and more particularly to a reinforced heat resistant metal product capable of sustaining high strength properties and high resistance to creep at elevated temperatures of up to about 1000 C. and higher for prolonged periods of time.

Considerable progress has been made in recent years in the development of cast and wrought nickel and cobalt base super-alloys for use in the production of power plant components for high powered thermal engines such as turbines, rockets, jets and the like. While these alloys have added measurably to the scientific development of such engines, increased operating temperatures of the more recently developed thermal engines to improve their power rating have placed considerable burden on these alloys. It was found that these alloys had definite temperature limitations in that they tended to soften, weaken and creep appreciably at temperatures above 900 C.

The typical wrought super-alloy generally comprises a solid solution alloy based on the metals nickel and/or cobalt and containing chromium as essential alloying ingredient together with hardening elements to stiifen the alloy for use at high temperatures. Generally, the stifiening may be achieved in several ways: (1) by hardening the solid solution matrix by employing such matrix hardening elements as molybdenum, tungsten, niobium, etc., (2) by employing special elements capable for forming compounds of low solubility which precipitation-harden the alloy, for example titanium, aluminum, zirconium, carbon, etc., (3) by employing other elements which form a second phase upon solidification which hardens the alloy, for example a phase based on carbon as might be obtained in a cast alloy. The hardening by the second method is achieved by heat treatment and may be employed to augment the hardening of the first method. Generally, most cast or wrought super alloys are susceptible to precipitation hardening. The precipitation hardening elements in the alloy are taken into solid solution by heating the alloy to a high solution temperature, for example 1000 C. to 1250 C., followed by rapid cooling to keep the precipitation hardening elements in solution. The precipitation hardening is then achieved by reheating the alloy at a lower temperature, for example, within the range of about 550 C. to 850 C., for a time sufficient to produce a critical dispersion of a fine precipitate throughout the matrix which in the case of a precipitate based on nickel, aluminum and titanium is generally invisible, even at a magnification of 2000 times and higher when achieving maximum benefit. Such alloys in the hardened conditions exhibit improved resistance to creep at elevated service temperatures up to about 900 C. However, at higher temperatures, the alloys tend to soften due to two effects. If the service temperature is in the neighborhood of about 850 to 900 C. or slightly higher,

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the alloys tend to soften due to over-aging. This phenomenon is believed to be due to growth and coalescence of the fine precipitate to large, coarse particles which is generally accompanied by a falling off in hardness and lower resistance to creep. Moreover, when the service temperature is in the neighborhood of 1000 to 1100 C. and higher, the precipitate begins to go into solid solution and the alloy softens. When the alloy softens because of the foregoing reasons, it loses its ability to sustain high static and/or dynamic stresses and deforms too readily. Furthermore, such alloys tend to form abnormally large grains at the high temperatures and become embrittled. Because tolerances and clearances of rotating and stationary members of thermal engines must be kept extremely small, any variation from normal creep can be dangerous and lead to serious damage of the power plant, even to the extent where engine performance may be impaired or the engine totally destroyed.

In an attempt to overcome the foregoing difficulties, super-alloys were proposed with higher amounts of hardening elements, e.g. carbon, or titanium plus aluminum, to further stiffen them so as to increase their sustaining power at elevated temperatures. While this was helpful to a certain extent, the stiffened alloys generally had lower ductility which was accompanied by a low resistance to impact. Moreover, the alloys could not be worked easily and usually were subject to cracking during the hot working operations. This was especially true when the super-alloys contained particularly high amounts of matrix hardening elements, e.g. tungsten, molybdenum, etc., and/ or high amounts of precipitation-hardening elements such as titanium, aluminum, zirconium, etc.

In a further attempt to improve the high temperature stability of super-alloys, slip-inhibiting compounds were employed. This was achieved by utilizing powder metallurgical techniques. The slip inhibiting compound which must have a high melting point and a low degree of solubility in the solid solution matrix of the heat resistant alloy, is mixed with a heat resistant alloy powder, such as a powder comprising nickel and 20% chromium, consolidated into a compact, and the compact then hot worked into the desired shape, for example by hot extrusion. The compound which is dispersed throughout the alloy works as a recovery inhibitor, that is it acts as a deterrent to recrystallization and to abnormal grain growth. As long as the compound is stable and does not decompose substantially at elevated temperatures, the alloy containing the dispersed compound is capable of sustaining its mechanical properties for prolonged periods of time at elevated temperatures that normally cause the more usual heat resistant alloys to soften and creep appreciably. This is because the slip-inhibiting compound has a stiifening effect on the alloy.

Unfortunately, when used in the alloy in amounts to confer maximum stiffness and rigidity, the hot working properties of the alloy are adversely affected, thus making the alloy very difficult to shape into buckets, turbine nozzle vanes, etc. Yet, on the other hand, if the alloys are hot workable at the usual forging temperatures, e.g. 1100 C. to 1325 C., the alloys would not be prone to exhibit the maximum possible creep resistance at 1000 C. and above. The higher the resistance to creep is, the more difficult it is to forge the alloy. The problem comes down to the utilization of the slip-inhibiting effect to the fullest extent in order to improve and/or sustain cree resistance while at the same time maintaining the forgeability of the alloy for fabrication purposes.

Although various methods have been proposed to overcome the foregoing difficulties, none, as far as we are aware, has so far been entirely successful.

A method has now been discovered for producing, by hot working, reinforced metal products containing relatively high amounts of slip-inhibiting phases which normally make the alloy difficult to hot work. The method is particularly applicable to heat resistant alloys of the super-alloy type based on at least one iron-group metal, preferably nickel and/or cobalt. The method is also applicable to other heat resistant materials, for example alloys based on molybdenum, chromium, niobium, tantalum, platinum, and generally metals having melting points above 1250 C.

It is the object of the present invention to overcome the fabrication limitations inherent in the working of heat resistant alloys containing disperse slip-inhibiting hard phases.

Another object is to provide a method for producing by hot working certain heat resistant alloys, for example carbon-containing cobalt-base alloys with hard carbide phases, which heretofore could only be produced adequately by casting.

Other objects will become more apparent from the following description.

Generally speaking, the present invention provides a method of producing by solid fabrication heat resistant alloys based on a ductile metal having a melting point of at least 1250 C., preferably alloys based on at least one iron group metal containing slip-inhibiting hard phases which normally render such alloys difficult to work. From the broad aspect, the invention comprises forming a substantially unalloyed mixture of the desired alloying constituents, the base metal or a simple alloy thereof being in the ductile state and constituting preferably at least 60% of the mixture, and more preferably at least 75%, the remaining constituents comprising alloying and hard phase-forming ingredients which confer heat resisting and slip inhibiting properties to the finally produced alloy, this being achieved by diffusion and chemical reaction processes brought about by appropriate heat treatment.

In order to achieve the results of the invention, it is important that the hot working be done before the ductile metal or alloy making up the major composition of the alloy has appreciably alloyed with the other ingredients mixed therewith and before any disperse hard phases have formed. After the desired shape has been obtained, the resulting hot worked metal is then subjected to a high temperature diffusion heat treatment not exceeding the melting point of any one of the ingredients or compounds or phases present to enable the metal to alloy with the alloying ingredients and the hard phaseforming ingredients to react with each other to form the desired slip-inhibiting phase. If the alloy desired is a cobalt-base alloy containing chromium, tungsten, small amounts of nickel, and amounts of carbon normally detrimental to the hot working of the alloy, say about 1%, the ingredients in this case would be mixed as powders in the elemental state or the processing could start with a simple ductile alloy powder based on the system of Co-Cr-W or Co-Cr to shorten alloying time and minimize formation of course grains. If elemental cobalt powder is used, it would provide the necessary plasticity during hot working until the desired shape is achieved before appreciable alloying occurs between the cobalt and the elements chromium, tungsten and nickel. The carbon is finely dispersed throughout the mixture and, as long as it does not react appreciably with chromium and/or tungsten to form carbide during the early stages of the hot working operation, it does not appreciably adversely affect the hot working of the mixture. After hot working is completed, the resulting material is then subjected to a high temperature diffusion heat treatment to effect alloying between cobalt, nickel, some of the chromium and some of the tungsten, while portions of the chromium and tungsten react with the carbon to form carbides, the amounts of each being determined by their relative free energies of formation and the law of mass action. The resulting carbide hard phase is substantially uniformly and finely distributed throughout the alloy. In this instance the chromium and tungsten behave as alloying ingredients with the cobalt as well as hard phase-forming ingredients with the carbon. The mixture could contain small amounts of either niobium, titanium, zirconium or hafnium or combinations of these metals as carbide formers.

An alloy formed in the foregoing manner differs from the same alloy produced by casting in that it is free from dendrites and massive carbide segregation. It is the dendritic carbide structure that renders such cast alloys brittle and difficult to hot work and imparts thereto low ductility and low resistance to impact.

As illustrative of the preferred embodiments of the invention, the following examples are given:

Example I A cobalt-base alloy, normally difiicult to hot work, which can be produced in accordance with the invention is one comprising 55% cobalt, 10% nickel, 15% tungsten, 18.75% chromium and 1.25% carbon. Finely divided powders of these materials of less than 40 microns, preferably less than 10 microns, are uniformly mixed together, cold pressed into a coherent billet of approximately 4 inches in diameter and 6 inches high at about 50 tons per square inch, and vacuum sealed snugly in a nickel container (or container of iron, or a nickel-chromium alloy), e.g. a container having a wall thickness of about 20 to 40 thousandths of an inch. The sealed compact is then heated to an extrusion temperature of about ll00 C. for a time just sufficient for it to come up to temperature so as to minimize diffusion reactions as much as possible. The heated sealed compact is then extruded at a pressure of about 100 tons per square inch at an extrusion ratio sufficient to effect a reduction in cross sectional area of at least about 50%, preferably about to Extrusion ratios of about 14:1 to 20:1 are usually used. The resulting product is then subjected to a diffusion heat treatment at a temperature of about 1250 C. for about 24 hours until alloying is effected between cobalt, nickel, some of the tungsten and some of the chromium. The remaining tungsten and chromium react with the finely dispersed carbon to form the slip inhibiting phases tungsten carbide, chromium carbide and possibly also a solid solution of these carbides. The metal skin remaining from the container is then removed.

Before the extruded material is subjected to the diffusion heat treatment, it may be desirable, while it is still workable, to put it through various shaping treatments, for example hot die forging to complicated turbine blade shapes which step is followed by the diffusion heat treatment to produce the desired composition.

Example II Another way of producing a dispersion hardened cohalt-base alloy is to use strong carbide formers, such as titanium and/or zirconium, as the starting hard phaseforming ingredient and a ductile cobalt alloy powder comprising about 69% cobalt, 25% chromium, and 6% molybdenum as the starting matrix metal. To produce an alloy containing about 10% by volume equivalent of TiC (6.25% by weight), 1.25% by weight carbon black, and 5% by weight of titanium powder are mixed with sufficient alloy (about 93.75% by weight) to bring the total up to the mixed powders having a particle size of minus 10 microns. The mixture is cold pressed into a coherent billet of approximately 2 inches in diameter and 3 inches high at about 50 tons per square inch and vacuum sealed in a sheath of nickel having a wall thickness of about one-sixteenth of an inch. The sealed compact is similarly heated as in Example I to a temperature of about 1100 C. for a time just sufficient for it to come up to temperature so as to minimize diffusion reactions as much as possible. The heated sealed compact is then extruded at a pressure of about 150 tons per square inch at an extrusion ratio of about 18:1. The resulting product is similarly subjected to a diffusion heat treatment at a temperature of about 1100 C. for about 12 hours until the hard phase-forming constituents have reacted to form a slip inhibiting titanium carbide phase. While the amount of carbon and titanium added is equivalent to a titanium carbide content of about 10% by volume, it will be appreciated that a small portion of the carbon may be shared by chromium and possibly by molybdenum. However, a major portion of it will combine with titanium to form the desired hard phase. After completion of the heat treatment, the outer nickel skin is removed by pickling, or by machining, grinding, or other suitable means.

Example 111 The present invention is also applicable to the production of a Ni-Cr-Fe heat resistant alloy containing about 5% by weight (about 10% by volume) of aluminum oxide. In producing the finely divided powder mixture (preferably less than 10 microns), the aluminum portion of the oxide is included in a starting alloy powder of 71.6 parts nickel, 18 parts chromium (4 Nizl Cr), and 2.6 parts aluminum. The oxygen portion is added and mixed with the alloy powder as 7.8 parts of Fe O The aluminum is stoichiometrically proportioned to oxygen in accordance with the formula A1 The unreacted mixture is equivalent to a final alloy composition by weight comprising about 71.6% nickel, 18% chromium, 5.7% Fe and 5% aluminum oxide (about by volume).

The mixture of the alloy and the Fe O is cold pressed at about 30 tons per square inch to form a coherent compact of about 9 inches in diameter and 12 inches high which is thereafter sheathed snugly into an iron container of one-eighth wall thickness which is vacuum sealed and then heated to an extrusion temperature of about 1200 C. for a time just sufiicient for it to come to temperature so as to minimize diffusion reactions between the ingi'edients as much as possible. The heated sealed compact is then extruded at a pressure of about 75 tons per square inch at an extrusion ratio of about 15:1 to form a rod. Similarly, as in Example I, the resulting extruded product is subjected to a diffusion heat treatment at a temperature of about 1100 C. for about 24 hours until reaction is elfected between the aluminum of the alloy and the oxygen of Fe O to form finely dispersed A1 0 the iron remaining from the reaction thereafter diffusing into the nickel-chromium alloy matrix surrounding the dispersed aluminum oxide hard phase. The amount of hard phase equivalent would be in the neighborhood of about 17% by volume of A1 0 It will be appreciated that a portion of the oxygen might tie up with some of the chromium to form an oxide thereof.

Before the extruded material is subjected to the diffusion heat treatment, it may be desirable, while it is still workable, to put it through various shaping treatments, for example hot die forging to complicated turbine blade shapes which step is followed by the diffusion heat treatment to produce the desired composition.

Example IV In producing an alloy similar to the one of Example III but containing about 5% by weight of Th0 (about 4.5% by volume), the same procedure would be used. Thus, the powder mixture would comprise about 95% and the balance Fe O proportioned stoichiometrically with the thorium to produce the desired amount of ThO To the starting alloy powder comprising 74.7% parts of nickel, 18.9 parts of chromium (4NizlCr) and 4.4 parts of thorium is mixed 2 parts of Fe O The shape is produced by cold pressing and hot extrusion as described in Example III. The extruded rod is then further hot worked to form electrical resistance heating elements which are then shaped for use in an electric furnace. The resulting product is then diffusion heat treated to react the Fe O with the thorium of the alloy to form the hard phase T uniformly dispersed throughout the alloy as in Example III. This heat treating may be carried out before the element is used in service or in situ during service.

Example V Titanium carbide and titanium nitride make excellent slip-inhibiting phases in nickel chromium alloys of the type illustrated in Examples III and IV. According to page 263 of the book Refractory Hard Metals by Dr. Paul Schwarzkopf and Dr. Richard Kieffer (published by The Macmillan Company, 1953), a solid solution of TiC and TiN at a mol ratio of 1:1 exhibits a maximum melting point on the melting point curve. Considering that TiN has a melting point of about 2930 C. to 2950" C., and TiC a melting point of about 3250 C., then the foregoing solid solution would have a higher melting point than 3250 C. In producing an alloy containing 8% by weight (about 12% by volume) of the solid solution hard phase equivalent and about 91% of an 80/20 nickel-chromium alloy plus small amounts of silicon, the following powder mixture could be employed: 73.6 parts of nickel, 18.4 parts of chromium, 2.3 parts of Si N 6.3 parts of titanium, and 0.8 part of carbon making up a total of about 101.4 parts. The powder is intimately mixed, cold pressed into a coherent compart at about 40 tons per square inch, encased in a container of iron and sealed vacuum tight therein. The sealed compact is heated to an extrusion temperature of about 1200 C. for a time suflicient for it to come to temperature so as to minimize diffusion reaction between the ingredients as much as possible. The heated sealed compact is then extruded at a pressure of about tons per square inch at an extrusion ratio of about 18:1 after which the resultant product is then heated at a temperature of about 1400 C. for about 12 hours until alloying is efiected between the free nickel and the free chromium as well as the small amount of silicon resulting from the reaction of Si N with Ti. The phase-forming constituents carbon and Ti as well as the nitrogen from Si N react to form TiC and TiN, a substantial portion of each further reacting with each other to form a solid solution of one into the other, otherwise referred to in the art as titanium cyanonitride. The iron skin remaining from the extrusion is then removed by machining or etching.

Before the extruded material is subjected to the diffusion heat treatment, it may be desirable, while it is still workable, to put it through various shaping treatments, for example hot die forging it to complicated turbine blade shapes which step followed by the diffusion heat treatment to produce the desired composition.

It will be apparent from the foregoing examples that a wide variety of compositions are possible, based on iron group metal such as iron-base, nickel-base and cobaltbase alloys. The hard phases which these alloys may contain and which are intended to fall within the scope of the present invention include such refractory compounds as carbides, silicides, borides and nitrides (including mixtures thereof) of the refractory metals chromium, tungsten, molybdenum, vanadium, niobium, tantalum, titanium, zirconium, and hafnium. Other hard phase refractory compound materials include oxides of aluminum, beryllium, cerium, magnesium, zirconium, titanium, thoriby Weight of 8 Starting alloy of njelgel-ehmmi 4h fi 75 um, etc. The hard phase-forming constituents may be used in their elemental form where possible or as a compound which will react with another element or compound to form the hard phase. As illustrated in Examples III and IV, the hard phase-forming constituents could be an easily reducible, relatively soft oxide like Fe O which is caused to react with a solid solution alloy powder containing aluminum to form the hard phase A1 Or it could be elemental titanium caused to react with carbon or with a metal nitride such as Si N as shown in Example V. The important thing is to have the whole powder mixture in a form in which a large portion of the mixture, preferably at least 60%, and more preferably at least 75%, comprises a ductile metal or alloy powder such as nickel, cobalt or iron, or simple alloys thereof, so that the mixture after consolidation will be workable at elevated temperature before any appreciable complex alloying or hardening sets in. The amount of hard phase may range up to about 35% by volume of the finally produced alloy and preferably from about 5% to 20% by weight.

While the foregoing examples have been limited to the production of iron group metal alloys, it will be appreciated that refractory metal alloys can also be hardened in similar manner. Such alloys may be based on niobium, for example binary alloys containing 5% to molybdenum and the balance niobium, or 5 to 10% tungsten and the balance niobium. Or, if desired, the alloy can be based on tantalum or even platinum or platinum group metals. For convenience, all of those metals and alloys having melting points above 1250 C. are referred to as refractory-base metals. As example of utilizing the foregoing metals, the following is given.

Example VI A suitable alloy is one comprising about 7.5% molybdenum and the balance niobium, the alloy being hardened by about 5% by weight of thoria. In producing the alloy, 7.5 parts of molybdenum, 2 parts of Fe O 4.4 parts of thorium and the balance niobium powder to bring the total to 100 parts are uniformly mixed together, cold pressed into a coherent compact at a pressure of about 40 tons per square inch, encased in a container of nickel, and sealed vacuum tight. The sealed compact is then heated to an extrusion temperature of about 1350 C. for a time sufficient for it to come to temperature so as to minimize diffusion reaction between the ingredients as much as possible. The heated extruded compact is then extruded through a refractory metal die, e.g. molybdenum, at a pressure of about 250 tons per square inch at an extrusion ratio of about :1 after which the resultant product is heated at a temperature of about 1450 C. for about 12 hours until alloying is effected between the free molybdenum and free niobium as well as the iron resulting from the reaction of Fe O with thorium to form the hard slip inhibiting phase thoria. The nickel skin remaining from the extrusion container is then removed by either machining or pickling.

As illustrative of the type of heat resisting alloy compositions that can be utilized in producing a hardened alloy, the following are given:

Examples of nickel-base alloys which can be dispersion hardened in accordance with the invention by starting with unalloyed ingredients or simple ductile alloys thereof include: 80% nickel and chromium; 80% nickel, 14% chromium and 6% iron; 15% chromium, 7% iron, 1% niobium, 2.5% titanium, 0.7% aluminum, and the balance nickel; 28% cobalt, 15% chromium, 3% molybdenum, 3% aluminum, 2% titanium, and the balance substantially nickel; 13.5% cobalt, 20% chromium, 4% molybdenum, 3% aluminum, 3% titanium, and the balance substantially nickel; 58% nickel, 15% chromium, 17% molybdenum, 5% tungsten and 5% iron; 95% nickel, 4.5% aluminum, and 0.5% manganese.

Examples of cobalt-base alloys which may similarly be produced include: 69% cobalt, 25% chromium and 6% molybdenum; 65% cobalt, 25 chromium, 6% tungsten, 2% nickel, 1% iron and other elements making up the balance of 1%; 56% cobalt, 10% nickel, 26% chromium, 7.5% tungsten; 51.5% C0, 10% Ni, 20% Cr, 15% W, 2% iron, and 1.5% manganese; 44% cobalt, 17% tungsten, 33% chromium, 2.25% carbon, and the balance other metals such as iron manganese.

Some of the iron-base matrix alloys also producible as dispersion hardened alloys include: 53% iron, 25% nickel, 16% chromium, and 6% molybdenum; 74% iron, 18% chromium and 8% nickel; 86% iron and 14% chromium; 82% iron and 18% chromium; 73% iron and 27% chromium, etc. Examples of steels which may be employed as matrix-forming metals include: SAE 1010 steel, SAE 1020 steel, SAE 1030 steel, SAE 1040 steel and SAE 1080 steel. Low medium and high alloy steels may also be employed, including the following; about 0.08% chromium, 0.2% molybdenum, about 0.30% carbon, and iron substantially the balance; about 5% chromium, 1.4% molybdenum, 1.4% tungsten, 0.45% vanadium, 0.35% carbon, and iron substantially the balance; about 8% molybdenum, 4% chromium, 2% vanadium, 0.85% carbon, and iron substantially the balance; about 18% tungsten, 4% chromium, 1% vanadium, 0.75% carbon, and iron substantially the balance; about 20% tungsten, 12% cobalt, 4% chromium, 2% vanadium, 0.80% carbon, and iron substantially the balance.

The matrix-forming metals or alloys broadly suitable in forming heat-resistant articles from iron group metals may contain up to about 30% by weight of a metal selected from the group consisting of chromium, molybdenum and tungsten, the sum of the metals of said group preferably not exceeding 40%, substantially the balance being at least one iron group metal selected from the group consisting of iron, cobalt and nickel, the sum of the iron group metals being preferably at least about 40% by weight of the matrix-forming alloy. If desired, the matrix-forming alloy may also contain up to about 8% total of at least one metal from the group niobium, tantalum and vanadium.

All of the above alloys may be produced in accordance with the invention to contain slip-inhibiting compounds such as refractory metal carbides, borides, silicides, nitrides as well as refractory oxides of the type recited hereinbefore.

As stated hereinbefore, the powder mixture from which the product is produced is first consolidated before it is hot worked or extruded. It is preferred that the mixture be consolidated to an apparent density of at least about 65 preferably as near as 90% as possible, before it is hot worked. While in general it would be preferred that the mixture be cold pressed, it will be appreciated that hot pressing can also be employed, provided an appreciable amount of alloying does not take place. In producing a compact of at least 65 apparent density by cold pressing, the pressures employed may range from 15 to 40 tons per square inch. When hot pressing is employed, the temperature will usually range from about 1000 to 1250 C. at pressures ranging from 1 to 20 tons per square inch, lower pressures being employed at higher temperature levels. When hot pressing is conducted, it should be carried out under protective conditions, e.g. in a reducing atmosphere, an inert atmosphere or even at subatmospheric pressure.

Likewise, when the compact is extruded, the conditions also should be protective to the materials forming the compact. Encasing the compact in an air-tight, evacuated, welded container, for example a sheath of iron or nickel, is one method of protecting the materials in the compact from oxidation, etc. Depending on the situation, extrusion pressures may range from about 40 to 250 tons per square inch over a temperature range of about 950 to 1350 C. for extrusion ratios ranging from about 14 to 1 to 20 to 1.

Some typical examples of the great variety of hardened alloys which can be produced by the invention are given by weight as follows:

PERCENT Fe Ni Co Cr W A1203 Cree: I TiC TN 1 A portion combined with a total of about 1.25% carbon as WC and 01302 and/or solid solutions thereof.

2 About 1.5% carbon tied up as CraCz.

Examples of products which can be made by the invention include structural parts and members for power plants, such as turbine blades, guide vanes, nozzles for jet engines, rockets, missiles and the like. Other products include structural parts and electric heating elements for furnaces, ovens, kilns, etc. In addition, the invention is also applicable to the production of tubes, rods and other shapes, for heat exchangers and conductors of fluid media.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. In a method of producing by solid state fabrication heat resistant alloys based on a ductile metal of melting point above 1250 C. containing slip-inhibiting hard phases which normally render such alloys difficult to hot work, the improvement which comprises forming a powder mixture of the desired alloying constituents with the ductile metal making up the major portion of at least 60% by weight of the composition of the mixture, the remaining constituents comprising alloying and hard phase-forming ingredients which confer heat resisting and slip-inhibiting properties to the finally produced alloy through subsequent heat treatment, the hard phase-forming ingredients being those which form at least one of the slipinhibiting compounds selected from the grou consisting of carbides, borides, silicides and nitrides of Cr, W, Mo, V, Nb, Ta, Ti, Zr, Hf and oxides of Al, Be, Ce, Mg, Zr, Ti and Th, consolidating said mixture into a hot workable compact and encasing it in a gas tight ductile metal sheath, hot shaping said sheathed compact to a desired shape at an elevated temperature under protective conditions by utilizing the ductile characteristics of said metal making up the substantial portion of said compact before appreciable alloying sets in, and then subjecting said hot worked shape to a diffusion and reaction heat treatment at an elevated temperature not exceeding the melting point of any one of the ingredients present to form the desired alloy composition with discrete slip-inhibiting hard phases distributed throughout said alloy.

2. In a method of producing by solid state fabrication heat resistant alloys based on a ductile metal comprising at least one iron-group metal containing slip-inhibiting hard phases which normally render such alloys diflicult to hot work, the improvement which comprises forming a powder mixture of the desired alloying constituents with the iron-group metal in the ductile state and constituting at least 60% of the mixture, the remaining constituents comprising up to by weight of at least one alloying ingredient from the group consisting of chromium, molybdenum and tungsten, the total amount of these metals not exceeding and hard phase-forming ingredients in amounts which will form up to about 35% by volume of slip-inhibiting hard phase selected from the group consisting of carbides, borides, silicides and nitrides of Cr, W, Mo, V, Nb, Ta, Ti, Zr, Hf and oxides of Al, Be, Ce, Mg, Zr, Ti and Th which together confer heat resisting and slip-inhibiting properties to the finally produced alloy through subsequent heat treatment, consolidating said mixture into a hot workable compact and encasing it in a gas tight ductile metal sheath, hot shaping said sheathed compact to a desired shape at an elevated temperature under protective conditions by utilizing the ductile characteristics of said iron-group metal making up the substantial portion of said compact before appreciable alloying sets in, and then subjecting said hot Worked shape to a difiusion and reaction heat treatment at an elevated temperature not exceeding the melting point of any one of the ingredients present to form the desired alloy composition with discrete slip-inhibiting hard phases distributed throughout said alloy.

3. In a method of producing by solid state fabrication heat resistant alloys based on at least one metal selected from the iron group consisting of iron, nickel and cobalt and containing slip-inhibiting hard phases which normally render such alloys difiicult to hot work, the improvement which comprises forming a powder mixture of the desired alloying constituents with the said group metal in the ductile state and constituting at least 60% of the mixture, the remaining constituents comprising up to 30% of at least one alloying ingredient from the group consisting of chromium, molybdenum and tungsten, the total amount of these metals not exceeding 40%, and hard phase-forming ingredients in amounts which will form up to about 35% by volume of the slip-inhibiting hard phase selected from the group consisting of carbides, borides, silicides and nitrides of Cr, W, Mo, V, Nb, Ta, Ti, Zr, Hf and oxides of Al, Be, Ce, Mg, Zr, Ti and Th in the finally produced alloy through subsequent heat treatment, consolidating said mixture into a hot workable compact and encasing it in an air tight ductile metal sheath, hot shaping said sheathed compact to a desired shape at an elevated temperature under protective conditions by utilizing the ductile characteristics of the iron-group metal making up the substantial portion of said compact before appreciable diffusion sets in, and then subjecting said hot worked shape to a difiusion and reaction heat treatment at an elevated temperature not exceeding the melting point of any one of the ingredients present to form the desired alloy composition with discrete slip-inhibiting hard phases distributed throughout said alloy.

4. In a method of producing by solid state fabrication heat resistant alloys based on a nickel-base alloy containing slip-inhibiting hard phases which normally render such alloys diflicult to hot work, the improvement which comprises forming a powder mixture of the desired alloying constituents with said nickel-containing constituent in the ductile state and constituting at least 60% of the mixture, the remaining constituents comprising up to 30% of at least one alloying ingredient from the group consisting of chromium, molybdenum and tungsten, the total amount of these metals not exceeding 40%, and hard phase-forming ingredients in amounts which will form up to about 35% by volume of the slip-inhibiting hard phase selected from the group consisting of carbides, borides, silicides and nitrides of Cr, W, Mo, V, Nb, Ta, Ti, Zr and Hf and oxides of Al, Be, Ce, Mg, Zr, Ti and Th in the finally produced alloy through subsequent heat treatment, consolidating said mixture into a hot workable compact, hot shaping said sheathed compact to a desired shape at an elevated temperature under protective conditions by utilizing the ductile characteristics of the nickel-containing mixture before appreciable diffusion sets in, and then subjecting said hot worked shape to a diffusion and reaction heat treatment at an elevated temperature not exceeding the melting point of any one of the ingredients present to form the desired alloy composition with discrete 1 1 slip-inhibiting hard phases distributed throughout said alloy.

5. In a method of producing by solid state fabrication heat resistant alloys based on a cobalt-base alloy containing slip-inhibiting hard phases which normally render such alloys difficult to hot work, the improvement which comprises forming a powder mixture of the desired alloying constituents with said cobalt-containing constituent in the ductile state and constituting at least 60% of the mixture, the remaining constituents comprising up to 30% of at least one alloying ingredient selected from the group consisting of chromium, molybdenum and tungsten, the total amount of these metals not exceeding 40%, and hard phase-forming ingredients in amounts which will form up to about 35% by volume of the slip-inhibiting hard phase selected from the group consisting of carbides, borides, silicides, and nitrides of chromium, tungsten, molybdenum, vanadium, niobium, tantalum, titanium, zirconium, hafnium, and oxides of aluminum, beryllium, cerium, magnesium, zirconium, titanium and thorium in the finally produced alloy through subsequent heat treatment, consolidating said mixture into a hot workable compact and encasing it in a gas tight ductile metal sheath, hot shaping said sheathed compact to a desired shape at an elevated temperature under protective conditions by utilizing the ductile characteristics of the cobalt-containing mixture before appreciable alloying sets in, and then subjecting said hot worked shape to a diffusion and reaction heat treatment at an elevated temperature not exceeding the melting point of any one of the ingredients present to form the desired alloy composition with discrete slipinhibiting hard phases distributed throughout the alloy.

6. In a method of producing by solid state fabrication heat resistant alloys based on an iron-base alloy containing slip-inhibiting hard phases which normally render such alloys difiicult to hot work, the improvement which comprises forming a powder mixture of the desired alloying constituents with said iron-containing constituent in the ductile state and constituting at least 60% of the mixture, the remaining constituents comprising up to 30% of at least one alloying ingredient selected from the group consisting of chromium, molybdenum and tungsten, the total amount of these metals not exceeding and hard phase-forming ingredients in amounts which will form up to about 35% by volume of the slip-inhibiting hard phase selected from the group consisting of carbides, borides, silicides, and nitrides of chromium, tungsten, molybdenum, vanadium, niobium, tantalum, titanium, zirconium, hafnium, and oxides of aluminum, beryllium, cerium, magnesium, zirconium, titanium and thorium in the finally produced alloy through subsequent heat treatment, consolidating said mixture into a hot workable compact and encasing it in a gas tight ductile metal sheath, hot shaping said sheathed compact to a desired shape at an elevated temperature under protective conditions by utilizing the ductile characteristics of the cobalt-containing mixture before appreciable alloying sets in, and then subjecting said hot worked shape to a diffusion and reaction heat treatment at an elevated temperature not exceeding the melting point of any one of the ingredients present to form the desired alloy composition with discrete slip-inhibiting hard phases distributed throughout the alloy.

References Cited in the file of this patent UNITED STATES PATENTS 2,123,416 Graham July 12, 1938 2,206,395 Gertler July 2, 1940 2,214,810 Chesterfield Sept. 17, 1940 2,225,424 Schwarzkopf Dec. 17, 1940 2,580,171 Hagglund Dec. 25, 1951 2,702,750 George Feb. 22, 1955 2,823,988 Grant Feb. 18, 1958 2,829,427 Tacvorian et a1. Apr. 8, 1958 FOREIGN PATENTS 574,170 Great Britain Dec. 27, 1945 

1. IN THE METHOD OF PRODDUCTING BY SOLID STATE FABRICATION HEAT RESISTANT ALLOYS BASED ON A DUCTILE METAL OF MELTING POINT ABOVE 1250*C. CONTAINING SLIP-INHIBITING HARD PHASES WHICH NORMALLY RENDER SUCH ALLOYS DIFFICULT TO HOT WORK, THE IMPROVEMENT WHICH COMPRISES FORMING A POWDER MIXTURE OF THE DESIRED CONSTITUENTS WITH THE DUCTILE METAL MAKING UP THE MAJOR PORTION OF AT LEAST 60% BY WEIGHT OF THE COMPOSITION OF THE MIXTURE, THE REMAINING CONSITIUENTS COMPRISING ALLOYING AND HARD PHASE-FORM ING INGREDIENTS WHICH CONFER HEAT RESISTING AND SLIP-INHIBITING PROPERTIES TO THE FINALLY PRODUCED ALLOY THROUGH SUBSEQUENT HEAT TREATMENT, THE HARD PHASE-FORMING INGREDIENTS BEING THOSE WHICH FORM AT LEAST ONE OF THE SLIPINHIBITING COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF CARBIDES, BORIDES, SILICIDES AND NITRIDES OF CR, E, MO, V, NB, TA, TI, ZR, HF AND OXIDES OF AL, BE, CE, MG, ZR, TI AND TH, CONSOLIDATING SAID MIXTURE INTO A HOT WORKABLE COMPACT AND ENCASING IT IN A GAS TIGHT DUCTILE METAL SHEATH, HOT SHAPING SAID SHEATHED COMPACT TO A DESIRED SHAPE AT AN ELEVATED TEMPERATURE UNDER PROTECTIVE CONDITIONS BY UTILIZING THE DUCTILE CHARACTERISICS OF SAID METAL MAKING UP THE SUBSTANTIAL PORTION OF SAID COMPACT BEFORE APPRECIABLE ALLOYING SETS IN, AND THEN SUBJECTING SAID HOT WORKED SHAPE TO A DIFFUSION AND REACTION HEAT TREATMENT AT AN ELEVATED TEMPERATURE NOT EXCEEDING THE MELTING POINT OF ANY ONE OF THE INGREDIENTS PRESENT TO FORM THE DESIRED ALLOY COMPOSITION WITH DISCRETE SLIP-INHIBITING HARD PHASES DISTRIBUTED THROUGHOUT SAID ALLOY. 